The sequence organization around a number of expressed genes in the genome of Drosophila melanogaster is being investigated. DNA segments of interest are isolated as cloned inserts by recombinant DNA techniques and characterized by restriction endonuclease digestion, Southern blotting methods; by electron microscopy; and by DNA sequence determination. Particular attention is paid to developmentally regulated genes - and within this category to the genes coordinately expressed during myogenesis.